As is well known, a press brake has an upper table at upper part of left and right side frames having a C-gap. To face the upper table in a vertical direction, the press brake has a lower table at lower part of the left and right side frames. A proper one of the upper and lower tables serves as a ram that is movable vertically. To vertically move the ram, the side frames are provided with left and right vertical driving units, respectively. An amount of vertical strain (deflection) on the left and right side frames is detected to compute pressing force applied by the vertical driving units. Based on a result of the computation, the pressing force of the vertical driving units is controlled. Related arts are, for example, Japanese Unexamined Patent Application Publications No. H05-57353 (Patent Literature 1) and No. H07-24530 (Patent Literature 2).